A switching strip system for capacitively detecting obstacles is known from U.S. Pat. No. 8,334,623 B2. The embodiment shown there in FIG. 14 has a bridge circuit, wherein the two conductors of a switching strip profile are connected in each case to one end of the bridge branch. However, the switching strip system is evaluated by comparing a voltage on the conductor located in front in the direction of detection with a reference signal unaffected by a change in the capacitance between the two conductors and an obstacle.
A sensor system for capacitively detecting obstacles is known from German laid-open specification DE 10 2008 005 783 A1, in which a control signal is fed into two conductive elements of a capacitive sensor. The inverted control signal is superposed with the signal of the conductor in front in the direction of detection and the superposition signal is adjusted to zero. If an obstacle is present in the detection area, it can be detected by means of the readjustment which is then required.